Are you aware of the Sierpinski fractal? here it is.
I recently saw a very interesting photo of a sea shell on a blog today.
(click the image to view the blog)
It turns out that the pigmentation in the shell follows fractal rules as to deciding the colouring.
The snail that grew the shell above is from the family Conidae. Other species have slightly different rules for pigmentation, but all produce their patterns by a method that can be modelled as cellular automata.